linux-kernel - Re: x86: get rid of the insane TIF_ABI

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Date:	Mon, 15 Feb 2010 17:17:52 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: x86: get rid of the insane TIF_ABI_PENDING bit

commit 05d43ed8a89c159ff641d472f970e3f1baa66318
Author: H. Peter Anvin <hpa@...or.com>
Date:   Thu Jan 28 22:14:43 2010 -0800

> --- a/arch/x86/include/asm/elf.h
> +++ b/arch/x86/include/asm/elf.h
> @@ -181,14 +181,8 @@ do {							\
>  void start_thread_ia32(struct pt_regs *regs, u32 new_ip, u32 new_sp);
>  #define compat_start_thread start_thread_ia32
>
> -#define COMPAT_SET_PERSONALITY(ex)			\
> -do {							\
> -	if (test_thread_flag(TIF_IA32))			\
> -		clear_thread_flag(TIF_ABI_PENDING);	\
> -	else						\
> -		set_thread_flag(TIF_ABI_PENDING);	\
> -	current->personality |= force_personality32;	\
> -} while (0)
> +void set_personality_ia32(void);
> +#define COMPAT_SET_PERSONALITY(ex) set_personality_ia32()

OK, but what about force_personality32? With this patch it becomes
unused?

> +void set_personality_ia32(void)
> +{
> +	/* inherit personality from parent */
> +
> +	/* Make sure to be in 32bit mode */
> +	set_thread_flag(TIF_IA32);
> +
> +	/* Prepare the first "return" to user space */
> +	current_thread_info()->status |= TS_COMPAT;

Can't understand why we need TS_COMPAT. I assume this is correct,
this was copied from flush_thread().

What TS_COMPAT actually means? I thought it just means "the task
is inside 32-bit syscall".

If a 64bit task execs a 32bit app, can't this TS_COMPAT break, say,
syscall_get_arguments() ?

Just curious, I don't really understand COMPAT issues anyway.

Oleg.

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